Arthropod-borne togaviruses, exemplified by the alphaviruses (e.g.,Sindbis) and flaviviruses (e.g., dengue-2), are maintained in nature by mandatory arthropod-vertebrate-arthropod -- transmission cycle. In arthropods these viruses produce a life-long persistent infection. Detailed comparative studies of Sindbis virus (SV) infection of A. albopictus and vertebrate cells have revealed that (1) mosquito cells favor emergence of temperature-sensitive (ts) small plaque mutants in persistent infection, (2) that these cells do not generate defective-interfering (DI) virus under conditions which lead to their production in vertebrate cells, (3) that, nevertheless, small (DI?) viral genomes appear in persistently infected cells. The nature of this low MW RNA will be compared with "DI RNA" from vertebrate systems previously characterized. Mutant clones of mosquito cells which are killed by SV will also be studied. Parallel experiments will be done in experimentally infected whole mosquitoes. RNA replication and morphogenesis of dengue-2 virus will be studied further. BIBLIOGRAPHIC REFERENCES: Stollar, V., Shenk, T.E., Koo, R., Igarashi, A., and Schlesinger, R.W. Established mosquito cell lines and the study of togaviruses. In "Invertebrate Tissue Culture Applications in Medicine, Biology and Agriculture," E. Kurstak, and K. Maramorosch, Eds., Academic Press, New York, 1976. p. 49-67. Stollar, V., Stollar, B.D., Koo, R., Harrap, K.A., and Schlesinger, R.W. Sialic acid contents of Sindbis virus from vertebrate and mosquito cells: Equivalence of biological and immunological viral properties. Virology 69, 104-115, 1976.